Investigation of Rotor Vibratory Loads of a UH-60A Individual Blade Control System

Wind tunnel measurements of a full-scale UH-60A Black Hawk main rotor with an individual blade control (IBC) system are compared with calculations obtained using a comprehensive rotorcraft analysis RCAS and a coupled CFD/CSD analysis using Helios. The effects of open-loop 3, 4, and 5/rev IBC on vibratory hub loads, rotor performance, and IBC actuator loads (pitch link loads) are investigated at high-speed, moderate-thrust and high-thrust, moderate-speed conditions. RCAS captures maximum vibratory hub load reduction values well for some cases, but phase is generally not well captured at all. The coupled analysis shows reasonably good correlation with the measured vibratory hub load variations with 3/rev IBC actuation at the high-speed condition. However, vibratory hub load correlation gets worse for 4 and 5/rev IBC actuations. IBC actuations also have a significant influence on rotor performance. Measured data show a maximum 2.2% rotor power reduction (3.9% increase in rotor lift to effective-drag ratio) using 3/rev IBC actuation with 0.9° amplitude at μ = 0.35. In general, the coupled analysis shows good correlation with the measured rotor power variations at both high-speed and high-thrust conditions. Half peak-to-peak IBC actuator load variations are well predicted by the coupled analysis only for the 3/rev IBC actuation at high speed. In general, correlation at the high-speed condition is better than for the high-thrust condition.